/**
 * Copyright  2017 ZTE Corporation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/**
 *
 */
package org.openo.commontosca.inventory.sdk.api.deferred;

import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

public class DeferredManager {

  private DeferredManager() {}

  @SafeVarargs
  public static <Result, Fail, Progress> Deferred<Collection<Result>, Fail, Progress> when(
      Deferred<Result, Fail, Progress>... deferreds) {
    return DeferredManager.when(Arrays.asList(deferreds));
  }

  public static <Result, Fail, Progress> Deferred<Collection<Result>, Fail, Progress> when(
      List<? extends Deferred<Result, Fail, Progress>> deferreds) {
    Iterator<? extends Deferred<Result, Fail, Progress>> iterator = deferreds.iterator();
    final Queue<Result> results = new ConcurrentLinkedQueue<Result>();
    Deferred<Result, Fail, Progress> deferred = iterator.next();
    for (; iterator.hasNext();) {
      final Deferred<Result, Fail, Progress> next = iterator.next();
      deferred = deferred.then(new PipeCallback<Result, Result, Fail, Progress>() {
        @Override
        public Deferred<Result, Fail, Progress> pipe(Result result) {
          results.add(result);
          return next;
        }
      });
    }
    return deferred.then(new PipeCallback<Result, Collection<Result>, Fail, Progress>() {
      @Override
      public Deferred<Collection<Result>, Fail, Progress> pipe(Result result) {
        results.add(result);
        return new DeferredObject<Collection<Result>, Fail, Progress>().resolve(results);
      }
    });
  }

}
